U.S. patent number 6,968,719 [Application Number 10/889,622] was granted by the patent office on 2005-11-29 for apparatus and methods for forming internally and externally textured tubing.
This patent grant is currently assigned to Packless Metal Hose, Inc.. Invention is credited to L. Robert Zifferer.
United States Patent |
6,968,719 |
Zifferer |
November 29, 2005 |
Apparatus and methods for forming internally and externally
textured tubing
Abstract
A machine may produce a tube having textured internal and
external surfaces in a single operation. Inner and outer knurling
tools may form the textured surfaces. The texturing of the internal
and external surfaces may be helical patterns of ribs and grooves.
The height of the ribs formed in the internal and external surfaces
may be less than about 35 mils. The angles of the patterns relative
to a longitudinal axis of the tube may be less than about
45.degree.. The angle of the helical pattern allows textured tubes
to be used as heat exchanger elements wherein flow is directed
substantially coaxial to the longitudinal axes of the tubes. The
helical pattern formed in the external surface may be oriented in a
right hand or left hand helical orientation. Similarly, the helical
pattern formed in the internal surface may be oriented in a right
hand or left hand orientation.
Inventors: |
Zifferer; L. Robert (Waco,
TX) |
Assignee: |
Packless Metal Hose, Inc.
(Waco, TX)
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Family
ID: |
26927956 |
Appl.
No.: |
10/889,622 |
Filed: |
July 12, 2004 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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902870 |
Jul 10, 2001 |
6760972 |
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Current U.S.
Class: |
72/96; 72/100;
72/105; 72/121; 72/703; 72/78; 72/98 |
Current CPC
Class: |
B21C
37/207 (20130101); Y10S 72/703 (20130101); Y10T
29/49385 (20150115); Y10T 29/5166 (20150115); Y10T
29/49382 (20150115); Y10T 29/49391 (20150115); Y10T
29/49384 (20150115) |
Current International
Class: |
B21B 019/08 () |
Field of
Search: |
;72/77,78,84,85,96,98,100,102,104,105,113,120,121,703 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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2515312 |
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Oct 1976 |
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DE |
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0882 939 |
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Dec 1989 |
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EP |
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1 448 901 |
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Sep 1976 |
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GB |
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07024522 |
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Jan 1995 |
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JP |
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Other References
International Search Report for International Application No.
PCT/US 01/29710, mailed on Apr. 2, 2002. .
International Search Report for International Application No.
PCT/US 01/48765, mailed on Jul. 22, 2002 (8 pages). .
International Preliminary Examination Report for PCT/US 01/48765,
mailed on Feb. 26, 2003 (8 pages). .
Written Opinion for PCT/US01/48675 mailed on Oct. 1, 2002 (7
pages). .
Communication Pursuant to Article 96(2) EPC for Application No. 01
996 265.3-1266 dated Jan. 30, 2004 (5 pages). .
Summons to Attend Oral Proceedings Pursuant to Rule 71(1) EPC for
Application no. 01996265.3-1266/1352204 dated Feb. 4, 2005 (9
pages)..
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Primary Examiner: Tolan; Ed
Attorney, Agent or Firm: Meyertons, Hood, Kivlin, Kowert
& Goetzel, P.C. Meyertons; Eric B.
Parent Case Text
PRIORITY CLAIM
This application is a divisional of Ser. No. 09/902,870 U.S. Pat.
No. 6,760,972 entitled "Apparatus and Methods For Forming
Internally and Externally Textured Tubing" filed on Jul. 10,
2001.
This application claims priority to U.S. Provisional Application
No. 60/234,458 entitled "Apparatus and Methods For Forming
Internally and Externally Textured Tubing," filed Sep. 21, 2000.
The above-referenced provisional application is incorporated by
reference as if fully set forth herein.
Claims
What is claimed is:
1. A texturing machine for forming a tube having a textured inner
surface and a textured outer surface, comprising: a mandrel; an
inner knurling tool coupled to the mandrel such that the inner
knurling tool is configured to rotate relative to the mandrel, and
wherein the inner knurling tool is configured to form a helical
pattern of grooves in the inner surface of the tube; an outer
knurling tool configured to form a helical pattern of grooves in
the outer surface of the tube, wherein a depth of the grooves
formed by the outer knurling tool is less than about 0.030 inches;
a positioner configured to adjust the position of the outer
knurling tool relative to the tube; and a drive configured to
rotate the outer knurling tool.
2. The texturing machine of claim 1, wherein a depth of the grooves
formed by the outer knurling tool is less than about 0.025 inches
and greater than about 0.004 inches.
3. The texturing machine of claim 1, wherein a depth of the grooves
formed by the outer knurling tool is less than about 0.020 inches
and greater than about 0.004 inches.
4. The texturing machine of claim 1, wherein inner knurling tool
and the outer knurling tool are configured to form crosshatched
texturing patterns in the inner surface and outer surface of the
tube.
5. The texturing machine of claim 1, wherein the pattern of grooves
formed by the outer knurling tool is oriented in a right hand
helical orientation.
6. The texturing machine of claim 1, wherein the pattern formed by
the inner knurling tool is oriented in a right hand helical
orientation.
7. The texturing machine of claim 1, wherein the pattern formed by
the inner knurling tool is oriented in a left hand helical
orientation.
8. The texturing machine of claim 1, wherein the pattern formed by
the outer knurling tool is oriented in a left hand helical
orientation.
9. The texturing machine of claim 1, wherein the outer knurling
tool is configured to be canted at an angle relative to a
longitudinal axis of the tube.
10. The texturing machine of claim 1, wherein the outer knurling
tool is configured to be canted at an angle relative to a
longitudinal axis of the tube in a range from 1.5.degree. to
5.degree..
11. A texturing machine for forming a tube having a textured inner
surface and a textured outer surface, comprising: an inner knurling
tool configured to form a helical pattern of grooves in the inner
surface of the tube in a first orientation, wherein a depth of the
grooves formed by the inner knurling tool is less than about 0.035
inches and greater than about 0.004 inches; an outer knurling tool
configured to form a helical pattern of grooves in the outer
surface of the tube oriented in a second orientation, wherein a
depth of the grooves formed by the outer knurling tool is less than
about 0.030 inches, and wherein the first orientation is in a
direction relative to the second orientation configured to produce
a crosshatched texturing pattern in the inner surface and outer
surface of the tube; and a positioner configured to adjust the
position of the outer knurling tool relative to the tube.
12. The texturing machine of claim 11, wherein a depth of the
grooves formed by the outer knurling tool is less than about 0.025
inches and greater than about 0.004 inches.
13. The texturing machine of claim 11, wherein a depth of the
grooves formed by the outer knurling tool is less than about 0.020
inches and greater than about 0.004 inches.
14. The texturing machine of claim 11, wherein the pattern of
grooves formed by the outer knurling tool is oriented in a right
hand helical orientation.
15. The texturing machine of claim 11, wherein the pattern formed
by the inner knurling tool is oriented in a right hand helical
orientation.
16. The texturing machine of claim 11, wherein the pattern formed
by the inner knurling tool is oriented in a left hand helical
orientation.
17. The texturing machine of claim 11, wherein the pattern formed
by the outer knurling tool is oriented in a left hand helical
orientation.
18. The texturing machine of claim 11, wherein the outer knurling
tool is configured to be canted at an angle relative to a
longitudinal axis of the tube.
19. The texturing machine of claim 11, wherein the outer knurling
tool is configured to be canted at an angle relative to a
longitudinal axis of the tube in a range from 1.5.degree. to
5.degree..
Description
BACKGROUND
1. Field of the Invention
The present invention generally relates to extended surface area
tubing. The present invention also generally relates to a machine
that produces textured surfaces on both inner and outer surfaces of
a tube. The textured surfaces may be patterns of ribs and grooves
formed in the inner and outer surfaces of the tube.
2. Description of Related Art
A heat exchanger tube may be used in a process that transfers heat
between a first fluid inside the heat exchanger tube and a second
fluid outside of the heat exchanger tube. The efficiency of heat
transfer between the first fluid and the second fluid may be a
complicated function that depends on the characteristics of the
fluids, on the characteristics of the heat exchanger tube, and on
the characteristics of fluid movement relative to the heat
exchanger tube. The term "fluid" refers to a liquid, a gas, or a
combination of a liquid and a gas. A heat exchanger tube may also
be used to transfer heat between a fluid and a solid. The solid may
be located inside or outside of the tube.
Each end of a tube may be pointed. A pointed tube may have reduced
diameter cylindrical portions at each end of the tube that
transition to a larger diameter main body section of the tube. A
pointed tube may facilitate attachment of the tube to support
structures. The support structures may be tube sheets of a heat
exchanger. Tube sheets may support several tubes within a shell of
a tube-and-shell heat exchanger. Fluid that is directed past
outside surfaces of tubes of a tube-and-shell heat exchanger may
flow in a direction that is substantially coaxial to a longitudinal
axis of the shell of the heat exchanger. Tubes having pointed ends
may be easier to position and seal to support structures than are
tubes that do not have pointed ends. U.S. Pat. No. 5,311,661, which
issued to Zifferer and which is incorporated by reference as if
fully set forth herein, describes an apparatus that may be used to
form heat exchanger tubes having pointed ends.
It is desirable to maximize the heat transfer rate across a wall of
a tube of a heat exchanger. Increasing the surface area of a tube
may increase the heat transfer rate across the tube. Also,
directing fluid flow past and through a tube in desired fluid flow
patterns may increase the heat transfer rate across the tube.
One method of increasing the surface area of a tube is to attach
fins to an outer surface of the tube. Fins may be attached to a
tube after the tube is formed, or fins may be formed in the outer
surface of the tube. Fins may be formed on the outer surface of a
tube by a finning tool of a finning machine. A finning tool
typically includes three or four disks mounted on an arbor. The
disks form a spiraled flight of fins on an outer surface of a tube
during use. The fins formed by a finning tool may have heights that
are greater than about 30 mils (0.030 inches). Generally, the fins
formed by a finning tool are oriented substantially perpendicular
to the longitudinal axis of the tube. A small amount of skew from a
true perpendicular orientation allows the finning tool to provide a
driving force to the tube that moves the tube through the finning
machine.
Fins may be oriented substantially perpendicular to a longitudinal
axis of the tube, or the fins may be oriented substantially
parallel to the longitudinal axis of the tube. Fins on an outer
surface of a tube that are substantially perpendicular to a
longitudinal axis of the tube may be used in heat transfer
applications where fluid flow is directed substantially
perpendicular to the longitudinal axis of the tube. Heat exchanger
tubes of condensers and evaporators may be finned tubes wherein the
fins are oriented substantially perpendicular to longitudinal axes
of the tubes. Fins that are oriented substantially parallel to a
longitudinal axis of a tube may be used in heat transfer
applications where fluid flow is directed substantially coaxial to
the longitudinal axis of the tube. Tubes having fins that are
oriented substantially parallel to longitudinal axes of the tubes
may be used in tube and shell heat exchangers.
Another method of increasing the surface area of a heat exchanger
tube is to texture the inner surface of the tube. A knurling tool
may be used to form a groove and rib pattern on an inner surface of
a tube. The knurling tool may be placed within the tube. Force may
be applied to an outer surface of the tube to press the inner
surface of the tube against the knurling tool. Pressing the inner
surface of the tube against the knurling tool forms a knurl pattern
on the inner surface of the tube.
A finning tool and a knurling tool may be used in combination to
form a tube that has a finned outer surface and a knurled inner
surface. U.S. Pat. No. 4,886,830, which issued to Zohler and which
is incorporated by reference as if fully set forth herein,
describes a method of forming a tube that has a finned outer
surface and a knurled inner surface.
An alternate method of texturing a tube is to form a desired
pattern of ribs and grooves on surfaces of a flat metal plate. The
plate may then be rolled into a cylindrical shape. A weld may be
formed to join the ends of the plate together and form a tube. U.S.
Pat. No. 5,388,329, which issued to Randlett et al., describes a
method of manufacturing an extended surface heat exchanger tube
using a rolled and welded metal plate.
A heat transfer rate across a tube may be increased by directing
fluid flow in a desired flow pattern through and by the tube. A
desired flow pattern may increase internal mixing of the fluid. A
desired flow pattern may promote non-laminar fluid flow of one or
both of the heat exchange fluids. In a straight, smooth-walled
cylindrical tube, fluid may flow past or through the tube in a
laminar flow pattern. Laminar fluid flow may develop a boundary
layer at a wall of the heat exchanger tube. The boundary layer may
inhibit heat transfer throughout the fluid. Non-laminar fluid flow
may minimize the formation of a boundary layer and promote internal
mixing of the fluid so that heat transfer takes place throughout
the fluid.
One method that may be used to obtain a desired fluid flow pattern
is to change the geometrical configuration of the surfaces of a
heat exchanger tube. The geometrical configuration of the surfaces
of a heat exchanger tube may be changed by texturing the surfaces
of the tube. Texturing the surfaces of the tube may increase the
heat transfer surface area of the tube and promote internal mixing
of fluid that flows through or by the tube.
SUMMARY
Inner and outer surfaces of a tube may be simultaneously textured
with a texturing machine. The texturing machine may include an
outer knurling device and an inner knurling device. The knurling
devices may be used to form grooves in inner and outer surfaces of
a tube. The depth of the grooves may be less than about 35 mils
(0.035 inches), and are preferably less than about 25 mils. The
depth of the grooves may be greater than about 4 mils. The grooves
formed in the outer surface of the tube may have a different depth
and a different pattern than the grooves formed in the inner
surface of the tube. The grooves formed in the surfaces of the tube
may increase the surface area of the tube, promote internal mixing
of fluid that flows by or through the tube, and inhibit formation
of stagnant areas of fluid adjacent to inner and outer surfaces of
the tube. The grooves may be formed in a helical pattern about a
longitudinal axis of the tube. The angles of the helical patterns
formed in the inner and outer surfaces of the tube may be less than
about 45.degree. relative to the longitudinal axis of the tube.
Angle patterns that are less than about 45.degree. relative to the
longitudinal axis of the tube may allow the tube to be used as a
heat exchanger element wherein fluid flows by and through the tube
in directions that are substantially coaxial with the longitudinal
axis of the tube.
Texturing in an outer surface of a tube may be formed in a helical
pattern by a texturing machine. An angle of the pattern relative to
a longitudinal axis of the tube may be less than 90.degree., and is
preferable less than about 45.degree.. The angle of the pattern
relative to a longitudinal axis of the tube may be greater than
about 2.degree.. Texturing in an inner surface of the tube may also
be formed in a helical pattern. An angle of the inner tube surface
pattern relative to a longitudinal axis of the tube may be less
than about 90.degree., and may preferably be between about
5.degree. and 45.degree.. The angle of the inner tube surface
pattern relative to a longitudinal axis of the tube may preferably
be about 30.degree..
An embodiment of a texturing machine may be used to form a
texturing pattern in an outer surface of a tube that is oriented in
an opposite direction to a texturing pattern formed in an inner
surface of the tube. For example, a pattern formed in an outer
surface of a tube may be a 20.degree. right-hand helical
orientation of grooves, while a pattern formed in an inner surface
of the tube may be a 30.degree. left-hand helical orientation of
grooves. In an alternate embodiment, the angle pattern in the outer
tube surface may be formed in a left-hand helical orientation, and
the angle pattern in the inner tube surface may be formed in a
right-hand helical orientation. The oppositely oriented patterns
may cause the formation of a crosshatched pattern in the outer and
inner surfaces of the tube. The crosshatched pattern may be a
result of grooves being formed in the outer surface when ribs are
formed on the inner surface. Similarly, grooves may be formed in
the inner surface when ribs are formed on the outer surface.
Embodiments of texturing machines may form helical patterns in
tubing that are in the same orientation. For example, helical
patterns in inner and outer tube surfaces may both be formed in
right-hand helical orientations. Helical patterns in inner and
outer tube surfaces may also both be formed in left-hand helical
orientations.
An outer knurling device of a texturing machine may include one or
more knurling tools. In an embodiment, the outer knurling device
includes three knurling tools that are offset from each other by
120.degree.. The outer knurling tools may be connected to drive
mechanisms. When the drive mechanisms are engaged, the knurling
tools rotate. The outer knurling device may also be coupled to a
mechanism that brings the knurling tools into contact with a tube.
When the knurling tools are brought into contact with a tube and
when the drive mechanisms are engaged, the knurling tools rotate
and form a helical pattern of grooves in an outer surface of the
tube. The rotation of the knurling tools may drive the tube through
the texturing machine.
In an embodiment, an angle of each outer knurling tool of a
texturing machine may be adjustably positionable relative to a
longitudinal axis of a tube positioned within the texturing
machine. The outer knurling tools may be angled from about
0.5.degree. to about 4.5.degree. in 0.5.degree. increments. The
lower ends of the knurling tools may be positioned close to an exit
end of the texturing machine. Each outer knurling tool may be set
at the same angle. The set angle of the outer knurling tools may
determine the feed rate of a tube through the texturing machine.
For a tube that is made of a material that is difficult to work,
e.g. titanium or cupro-nickel, a small set angle may be preferred.
For a tube that is made of a material that is easy to work, e.g.
copper, a larger set angle may be preferred so that there is a
higher production rate of textured tubing from the texturing
machine.
A tube may be positioned over an inner knurling device. The inner
knurling device may be positioned beneath an outer knurling device
of a texturing machine. The inner knurling device may be rotatively
coupled to a mandrel. When a knurling tool or knurling tools of an
outer knurling device are brought into contact with an outer
surface of a tube, the outer knurling device may press an inner
surface of the tube against the inner knurling device. When a drive
mechanism or drive mechanisms of the knurling device are engaged to
move the tube through the texturing machine, the inner knurling
device forms texturing on the inner surface of the tube as the
outer knurling device forms texturing on the outer surface of the
tube.
A tube that is to be textured by a texturing machine may be placed
over a mandrel of the machine so that a portion of a first end of
the tube extends beyond the outer knurling device. The outer
knurling device may be pressed against the tube to press an inner
surface of the tube against the inner knurling device. A drive or
drives may be engaged to move the tube through the machine so that
the knurling devices form textured inner and outer tube surfaces.
The drive or drives may be disengaged before the outer knurling
device reaches a second end of the tube. Placing a portion of the
first end of the tube beyond the outer knurling device and
disengaging the knurling machine before reaching the second end of
the tube leaves un-textured portions of tubing at each end of the
tube. Un-textured portions of tube may allow the tube to be easily
attached and sealed to support structures, such as tube sheets of a
heat exchanger.
Each end of a textured tube may also be pointed by a pointing
machine to promote easy attachment of the tube to support
structures. To point an end of a tube, the end of the tube may be
brought into contact with a tube-pointing die. The tube-pointing
die may form a frustro-conical section and a cylindrical section
having a reduced diameter at the end of the tube.
A texturing machine may form a tube having inner and outer textured
surfaces in a single operation. The textured surfaces may have
increased surface area, and the textured surfaces may promote
internal mixing of fluid that flows past the surfaces. Inner and
outer textured surfaces may increase the effective heat transfer
coefficient of the tube as compared to an un-textured tube of the
same diameter.
A texturing machine may form grooves in inner and outer surfaces of
a tube that are less than about 35 mils. The depth of the grooves
may inhibit formation of stagnant fluid areas adjacent to the inner
and outer surfaces of the tube while still promoting internal
mixing of fluid flowing by or through the tube.
A texturing machine may be used to form texturing patterns having a
variety of angle patterns and orientations. Different knurling
devices may be installed in the texturing machine to form different
patterns and different orientations. The angle of the patterns
formed in the inner and outer tube surfaces may be less than about
90.degree. relative to a longitudinal axis of the tube. The angle
of the patterns formed in the inner and outer tube surfaces may
preferably be less than about 45.degree. relative to the
longitudinal axis of the tube to promote efficient heat transfer
across the tube when the flow of fluid by and through the tube is
directed substantially coaxial to the longitudinal axis of the
tube. The texturing machine may be used to form a helical pattern
in an outer surface of a tube in a first direction that is opposite
in orientation to a helical pattern formed in an inner surface of
the tube. Oppositely oriented helical patterns may result in the
formation of a crosshatched pattern in the inner and outer surfaces
of the tube.
An angle of outer knurling tools relative to a longitudinal axis of
a tube positioned within a texturing machine may be adjustable.
Adjusting the angle of the knurling tools allows a user to control
throughput of tubing processed by the texturing machine. The
throughput of the machine may be controlled to compensate for
differences in hardness and workability of different types of
tubing.
A texturing machine may leave un-textured portions at each end of
the tube. The un-textured portions may allow the tube to be easily
attached and sealed to support structures. Also, end portions of a
textured tube may be pointed to allow the tube to be easily and
conveniently attached and sealed to a support structure. A tube may
be sealed to a support structure by a sealing method. The sealing
method may be, but is not limited to, welding or application of
sealant. Attaching a textured tube that has un-textured ends may be
easier to accomplish than attaching a textured tube with textured
ends because special procedures do not have to be implemented to
ensure that a seal is formed adjacent to all of the grooves and
ribs formed in the tube. A texturing machine may be sturdy,
durable, simple, efficient, reliable and inexpensive; yet the
machine may also be easy to manufacture, install, maintain and
use.
BRIEF DESCRIPTION OF THE DRAWINGS
Advantages of the present invention will become apparent to those
skilled in the art with the benefit of the following detailed
description of embodiments and upon reference to the accompanying
drawings in which:
FIG. 1 shows a representation of a front view of an embodiment of a
texturing machine;
FIG. 2 shows a perspective view of a cylindrical tube that may be
used as a blank during formation of a textured tube;
FIG. 3 shows a perspective view of a textured tube, including a cut
away portion that shows texturing on an inner surface of the
tube;
FIG. 4 shows a cross sectional view of the textured tube, taken
substantially along plane 4--4 of FIG. 3;
FIG. 5 shows an outside portion of a textured outside surface of a
tube wherein the helical pattern formed in the outer surface of the
tube is formed in a direction that is opposite to the direction of
the helical pattern formed in the inner surface of the tube;
FIG. 6 shows a side view of an embodiment of an inner knurling
tool;
FIG. 7 shows a perspective view of a head of a texturing
machine;
FIG. 8 shows an end view of an embodiment of a head of a texturing
machine with a mandrel and tube centrally positioned within the
head;
FIG. 9 shows a representation of a portion of an embodiment of a
texturing machine with canted or angled outer knurling tools;
FIG. 10 shows a diagrammatic representation of a tube pointing
machine;
FIG. 11 shows an end view of a tube-pointing die;
FIG. 12 shows a cross sectional view of a tube-pointing die taken
substantially along line 12--12 of FIG. 11 along with a
representation of a textured tube;
FIG. 13 shows a representation of a pointed tube with a cutout
portion that emphasizes the change in wall thickness due to the
pointing of the tube;
FIG. 14 shows a front view of a heat exchanger;
FIG. 15 shows an end view of a heat exchanger with an end cap of
the heat exchanger removed from the shell of the heat exchanger to
emphasize the tube pattern within the heat exchanger; and
FIG. 16 shows a partial cross sectional view of the heat exchanger
taken substantially along line 16--16 of FIG. 15, wherein the
textured tubes are not shown in cross section.
While the invention is susceptible to various modifications and
alternative forms, specific embodiments thereof are shown by way of
example in the drawings and will herein be described in detail. The
drawings may not be to scale. It should be understood, however,
that the drawings and detailed description thereto are not intended
to limit the invention to the particular form disclosed, but to the
contrary, the intention is to cover all modifications, equivalents
and alternatives falling within the spirit and scope of the present
invention as defined by the appended claims.
DETAILED DESCRIPTION
FIG. 1 shows a top view of texturing machine 20. The texturing
machine 20 may be used to texture both inner surface 22 and outer
surface 24 of a tube 26. FIG. 2 shows a perspective view of a
cylindrical tube 26 that may be used as a starting blank for
formation of a textured tube 28. FIG. 3 shows a representation of
textured tube 28. A portion of the tube 28 is cutaway to show the
texturing of the inner surface 22. FIG. 4 shows a cross sectional
view of the tube 28.
A texturing machine 20 may form a textured tube 28. Cylindrical
tube 26 may be used as a starting material to form a textured tube
28. The cylindrical tube 26 may have an outer diameter that is
greater than about 1/4 of an inch. In an embodiment, the outer tube
diameter of the cylindrical tubing stock 26 is about 11/2 inches.
Preferably, the cylindrical tube 26 is a metallic tube. In certain
embodiments, the cylindrical tubing stock 26 may be made of a high
thermal conductivity metal; including, but not limited to, copper,
brass, or aluminum. In other embodiments, the cylindrical tubing
stock 26 may be made of a corrosion resistant metal; including, but
not limited to, stainless steel, titanium, or titanium alloy.
Preferably, the cylindrical tube 26 used to form a textured tube 28
has a thin wall thickness. The tubing material may be chosen based
upon a number of factors including, but not limited to, material
cost, required heat transfer rate across the tubing, and corrosive
properties of fluids that contact the tubing. A length of the
cylindrical tube 26 may be reduced when the texturing machine 20
forms the tube into a textured tube 28.
A texturing machine 20 may simultaneously texture both an inner
surface 22 and an outer surface 24 of a tube 26. The texturing
formed in the inner and outer surfaces 22, 24 may be helically
formed patterns of grooves 30. Forming a pattern of grooves 30 in
the inner and outer surfaces 22, 24 may result in the formation of
ribs 32 between adjacent grooves. The angle of the helical pattern
of grooves 30 and ribs 32 in the inner surface 22 of a textured
tube 28 relative to longitudinal axis 34 of the tube may be less
than 90.degree., and preferably is less than 45.degree., and most
preferably is about 30.degree.. The angle of the helical pattern of
grooves 30 and ribs 32 in the inner surface 22 of a textured tube
28 relative to longitudinal axis 34 of the tube may be greater than
about 5.degree.. The angle of the helical pattern of grooves 30 and
ribs 32 in the outer surface 24 of the tube 28 relative to the
longitudinal axis 34 of the tube may be less than 90.degree., and
preferably less than about 45.degree., and most preferably is less
than about 30.degree.. The angle of the helical pattern of grooves
30 and ribs 32 in the outer surface 24 of the tube 28 relative to
the longitudinal axis 34 of the tube may be greater than about
2.degree..
An angle pattern of grooves 30 that is less than about 45.degree.
relative to a longitudinal axis 34 of a textured tube 28 may
inhibit stagnation of fluid that flows through or by the textured
inner and outer surfaces 22, 24 if the flow is directed
substantially coaxial to a longitudinal axis 34 of a tube 28. An
angle pattern of greater than about 45.degree. may allow the ribs
32 to act as baffles that inhibit fluid through the grooves 30 if
the flow is directed substantially coaxial to the longitudinal axis
34 of the tube 28. If the ribs 32 function as baffles, the ribs may
allow fluid within the grooves 30 to be substantially immobile or
stagnant. The angle pattern of textured inner surface 22 may be
substantially the same as the angle pattern formed in textured
outer surface 24. Alternately, the angle pattern of textured inner
surface 22 may be may be unequal to the angle pattern of outer
textured surface 24. For example, the inner surface 22 may have an
angle pattern of 30.degree. relative to a longitudinal axis 34 of
the tube 28, and the outer surface 24 may have an angle pattern of
20.degree. relative to the longitudinal axis of the tube.
The helical pattern formed by a texturing machine 20 in an inner
surface 22 of a tube 26 may be in a right-handed helical
orientation or a left-handed helical orientation. Similarly, the
helical pattern formed by a texturing machine 20 in an outer
surface 24 of a tube 26 may be in a right-handed helical
orientation or a left-handed helical orientation. The helical
patterns formed in the inner surface and outer surface 22, 24 of a
tube 28 may both have the same orientation. For example, the
helical pattern formed in the inner and outer surfaces 22, 24 may
both have right or left-handed helical orientations. FIG. 3 shows a
tube 28 wherein the helical pattern formed in the inner surface 22
and the outer surface 24 of the tube are oriented in the same
direction.
Alternatively, a helical pattern formed in a textured inner surface
22 may be oriented opposite to a helical pattern formed in a
textured outer surface 24. For example, the helical orientation of
the inner surface 22 may be a right-hand helical orientation while
the helical orientation of the outer surface 24 may be a left-hand
helical orientation. In an alternate embodiment, the helical
orientation of the inner surface 22 may be a left-hand helical
orientation while the helical orientation of the outer surface 24
may be a right-hand helical orientation. The opposite helical
orientations may produce a crosshatched pattern in the surfaces 22,
24 of the tube 28. FIG. 5 shows a representation of a portion of an
outer surface 24 of a tube 28 wherein the texturing machine 20
produced oppositely oriented helical orientations in the inner and
outer surfaces 22, 24. The crosshatched pattern may be a result of
indirect formation of grooves in the surfaces of the tube 26.
Grooves 30 may be indirectly formed in the inner surface 22 when a
texturing machine 20 forms ribs 32 on the outer surface 24.
Similarly, grooves 30 may be indirectly formed in the outer surface
24 when the texturing machine 20 forms ribs 32 on the inner surface
22. Grooves 30 in a surface that are formed as a result of ribs 32
being formed on an opposite surface may have different depths than
grooves that are directly formed in the surface by the texturing
machine 20.
A height between a bottom of a groove 30 and a top of a rib 32 of a
textured surface 22 or 24 may be less than about 35 mils, may
preferably be less than about 25 mils, and may be more preferably
be less than about 20 mils. The height between a bottom of a groove
30 and a top of a rib 32 may be greater than about 4 mil. In an
embodiment, the height of the ribs 32 formed in the outer surface
24 may be substantially the same as the height of the ribs formed
in the inner surface 22. In an alternate embodiment, the height of
the ribs 32 formed in the outer surface 24 may be different than
the height of the ribs formed in the inner surface 22. For example,
FIG. 4 shows an embodiment of a tube 28 wherein the height of the
ribs 32 in the outer surface 24 are of a height, which may be about
12 mils, which is different that a height of the ribs formed in the
inner surface 22, which may be about 20 mils.
A pattern formed in an inner tube surface 22 may be formed by inner
knurling tool 36 of a texturing machine 20. FIG. 6 shows a partial
representation of a cylindrical inner knurling tool 36. The
knurling tool 36 may include bore 37 through longitudinal axis of
the cylinder that allows the knurling tool to be coupled to the
texturing machine 20.
A pattern formed in the outer surface 24 of a textured tube 28 may
be formed by outer knurling tool 42, or by outer knurling tools. An
outer knurling tool 42 may substantially resemble an inner knurling
tool 36. The geometric properties of the knurling tools 36, 42,
such as outer diameter and length, may differ. The knurling tools
36, 42 form ribs 32 and grooves 30 in inner and outer surfaces 22,
24 of the tube 26 in opposite patterns to the patterns of ribs
formed in the surfaces of the knurling tools 36, 42. The knurling
tools 36, 42 may be made of materials that are harder than the
material of the tube 26 being textured. For example, the knurling
tools 36, 42 may be formed of C2 carbide and the tube 26 may be
formed of copper.
A knurling tool 36 or 42 may include a large number of grooves 38
and ribs 40 on an outer surface of the tool. For example, FIG. 6
depicts grooves 38 and ribs 40 in an inner knurling tool 36. In an
embodiment, an inner knurling tool 36 and an outer knurling tool 42
for a 11/2" diameter tube 26 each form 80 ribs 32 in the
circumference of the tube during texturing. Knurling tools 36 or 42
that form fewer or more ribs 32 in a tube 26 may also be used.
Also, a different number of ribs 32 may be formed in an outer
surface 24 of a tube 26 than are formed in an inner surface 22 of
the tube.
Different knurling tools 36, 42 may be interchangeable positioned
within a texturing machine 20. The ability to use different
knurling tools 36, 42 within a texturing machine 20 may allow
textured tubes 28 to be formed that have different rib heights,
different angle patterns, and/or different helical pattern
orientations. Tubes 28 with different rib heights, angle patterns,
and/or helical pattern orientations may be needed for different
heat transfer applications.
The inner knurling tool 36 and the outer knurling tools 42 may be
configured to form different types of grooves 30 and ribs 32. For
example, in an embodiment of a texturing machine 20, the inner
knurling tool 36 may be configured to form substantially "U" shaped
grooves 30, while the outer knurling tool 42 may be configured to
form substantially "V" shaped grooves. FIG. 4 shows an embodiment
of a textured tube 28 wherein the knurling tools 36, 42 formed
grooves 30 and ribs 32 of different shapes in the tube.
FIG. 1 shows a representation of a front view of texturing machine
20 that may be used to form a textured tube 28. The machine 20 may
include mandrel 44, tube support 46, head 48, drive shafts 50 and
drives 52. The machine 20 may also include a cooling system (not
shown) that inhibits overheating of the machine and a tube 26
during formation of a textured tube 28. The cooling system may
direct a stream of coolant against the tube 26 and portions of the
head 48 to cool and lubricate the tube and the machine 20. The
coolant may flow by gravity to a collection pan below the head
48.
A mandrel 44 may be a guide and support for a tube 26 that is
positioned within a texturing machine 20. A mandrel 44 may be a
tube or rod with an inner knurling tool 36 rotatively mounted to
the tube or rod near a first end of the mandrel. In an embodiment,
the inner knurling tool 36 is not driven, but is free to rotate. In
an alternate embodiment, the inner knurling tool 36 may be coupled
to a drive mechanism. A second end of the mandrel 44 may be fixedly
attached to support structure 54 of the texturing machine 20. The
knurling tool 36 may have a diameter that is less than a diameter
of the tube 26 to be textured. The mandrel 44 may position the
inner knurling tool 36 centrally within the head 48. A user may
slide a tube 26 that is to be textured over the inner knurling tool
36 and mandrel 44 so that the knurling tool supports a portion of
the weight of the tube. Also, the tube 26 may be partially
supported by a tube support 46.
A head 48 of a texturing machine 20 may include covers 56, end
plates 58, outer knurling tools 42, and positioners 60. FIG. 7
shows a perspective view of an embodiment of a head 48 of a
texturing machine 20. FIG. 8 shows an alternate view of the
embodiment of the head 48 of the texturing machine 20 shown in FIG.
7. The covers 56 may be made of polycarbonate, or other transparent
material. The covers 56 may allow a user to view the outer knurling
tools 42 and the tube 26 during texturing of the tube. The end
plates 58 and covers 56 may keep coolant within the head 48 during
formation of a textured tube 28. In the embodiment shown in FIGS. 7
and 8, the head 48 includes three outer knurling tools 42 that are
offset by 120.degree. relative to each other. Other embodiments may
include fewer or more knurling tools 42. The head may include a
positioner 60 for each knurling tool 42.
Positioners 60 of a head 48 may adjust the location of outer
knurling tools 42 towards or away from a tube 26 centrally
positioned within the head 48. In an embodiment, the positioners 60
may include hydraulically operated height adjustment cylinders. The
positioners 60 may be independently adjustable so that a distance
between each outer knurling tool 42 and a tube 26 centrally
positioned within the head 48 may be independently adjusted. The
positioners 60 may also be dependently adjustable so that a
distance between a tube 26 centrally positioned in the head 48 and
each knurling tool 42 may be simultaneously adjusted. When the
positioners 60 are in an initial position, the knurling tools 42
may be offset a distance from a tube 26 that is centrally
positioned within the head 48. The distance may allow a tube 26 to
be inserted onto the mandrel 44. The distance may also allow a
textured tube 28 to be removed from the texturing machine 20. When
the positioners 60 are engaged, the outer knurling tools 42 may be
moved towards the inner knurling tool 36. The positioners 60 may
press the outer knurling tools 42 against a tube 26 positioned over
the inner knurling tool 36. The positioners 60 may press the
knurling tools 42 against the tube 26 with enough force to press an
inner surface 22 of the tube 26 against the inner knurling tool
36.
Outer knurling tools 42 may be adjustable to establish a set angle
of the outer knurling tools relative to a longitudinal axis 34 of a
tube 26 positioned within the texturing machine 20. FIG. 9 shows a
representation of a portion of a head 48 of a texturing machine
wherein the set angle A of the outer knurling tools 42 relative to
longitudinal axis 34 of the tube 26 is approximately 2.5.degree..
FIG. 9 shows the portion of the head 48 before the positioners 60
press the knurling tools 42 against the tube 26. In an embodiment,
the set angles of outer knurling tools 42 may be adjusted from
about 0.5.degree. to about 5.degree. in 0.5.degree. increments.
Lower ends of the outer knurling tools 42 relative to the tube 26
are located closer to an exit end of the texturing machine 20.
Prior to using the texturing machine 20, each outer knurling tool
42 of the texturing machine may be set at the same set angle. The
set angles of the outer knurling tools 42 may be adjusted to
control the throughput rate of tubing 26 in the texturing machine
20. A large set angle may allow for a greater throughput than a
smaller set angle. The material of the tube 26 may also be taken
into consideration when setting the set angle of the outer knurling
tools 42. A tube 26 made of a difficult to work material, such as
titanium, may need a slow throughput time in the texturing machine
20. The set angle of the outer knurling tools 42 may be adjusted to
a small angle for a difficult to work material. A tube 26 made of
an easy to work material, such as copper, may be processed at a
high throughput rate. The set angle of the outer knurling tools 42
may be adjusted to a large angle for easy to work materials.
A drive shaft 50 may be coupled to each outer knurling tool 42.
Each drive shaft 50 may be coupled to a drive 52. In an embodiment,
each drive 52 is an electrically operated motor. The drives 52 may
be engaged to rotate the drive shafts 50 and the outer knurling
tools 42. The rotating outer knurling tools 42 may texture the
outer surface 24 of the tube 26 and propel the tube through the
texturing machine 20.
Texturing machine 20 may be used to form a textured tube 28.
Cylindrical tubing stock 26 may be placed over the inner knurling
tool 36 of the mandrel 44. The tube 26 may be pushed down a length
of the mandrel 44 so that the tube is supported by the mandrel and
by tube support 46. A portion of the tube 26 may extend beyond the
inner and outer knurling tools 36, 42. A portion of the tube 26 may
be centrally positioned within the head 48. The inner surface 22
and outer surface 24 of the portion of the tube 26 that extend
beyond the knurling tools 36, 42 will not be textured by the
machine 20. Each outer knurling tool 42 may be adjusted so that
outer knurling tools are canted at a desired set angle relative to
the longitudinal axis 34 of the tube 26. The drives 52 may be
engaged to rotate the outer knurling tools 42. Positioners 60 may
be engaged to press the outer knurling tools 42 against the outer
surface 24 of the tube 26. Pressing the outer knurling tools 42
against the outer surface 24 of the tube 26 may press the inner
surface 22 of the tube against the inner knurling tool 36. Pressing
the inner surface 22 of the tube against the inner knurling tool 36
may form grooves 30 and ribs 32 in the inner surface of the tube
26. Pressing the outer knurling tools 42 against the outer surface
24 of the tube 26 may form grooves 30 and ribs 32 in the outer
surface of the tube.
The rotating outer knurling tools 42 drive the tube 26 through the
head 48 so that texturing is formed on the inner surface 22 and
outer surface 24 of the tube. The drives 52 may be disengaged to
stop the rotation of the outer knurling tools 42 before the
knurling tools texture an end portion of the tube 26. The drives 52
may be disengaged at a point during the formation of a textured
tube 28 when a length of an un-textured portion 62 of a first end
of the tube is about equal to a length of an un-textured portion 64
of a second end of the tube. The positioners 60 may be disengaged
so the positioners return to initial positions. The textured tube
28 may be removed from the texturing machine 20.
After forming textured inner and outer surfaces 22, 24 of a tube
28, the tube may be pointed. FIG. 10 shows a diagrammatic view of
tube pointing machine 100. The tube pointing machine 100 may
include drive 102 and die housing 104. The drive 102 may push an
end of a textured tube 28 against pointing die 106 that is
positioned within the die housing 104. The drive 102 may be, but is
not limited to, a hydraulic mechanism or a mechanical mechanism
that advances the position of the tube 28 longitudinally into the
die housing 104. Alternately, the drive 102 may move the die 106
and die housing 104 against the tube 28.
FIG. 11 shows an end view of pointing die. FIG. 12 shows a cross
sectional portion of a pointing die 106. A pointing die 106 may
have frustro-conical surface 108 that leads to cylindrical opening
110. The cylindrical opening 110 may include a chamfered rear
portion 112. The die 106 may be made of a metal having a hardness
greater than the hardness of the tubing 28 to be pointed. For
example, stainless steel may be used as a die material for a
pointing die 106 that will point a textured copper tube 28.
To point a textured tube 28, an end of the tube and a die 106 are
pressed together by a drive 102. The frustro-conical surface 108 of
the die 106 may reduce the tube diameter as the tube 28 and die are
pressed together. The frustro-conical surface 108 may form
frustro-conical portion 66 of textured tube 28 that tapers the tube
from a large diameter to a smaller diameter. A leading portion of
the tube 28 may be forced into the opening 110 of the die 106. The
opening 110 may form cylindrical portions 68 at each end of the
tube 28. Each cylindrical portion 68 has a reduced tube diameter as
compared to a principal diameter of the tube 28. In an embodiment,
the cylindrical portions 68 of the tube 28 are un-textured
surfaces. In alternate embodiments, the cylindrical portions 68 may
be textured, or partially textured surfaces. The frustro-conical
portions 66 of the tube 28 may be textured, partially textured, or
un-textured surfaces.
A tube pointer die 106 may be a component of a pointing machine.
The pointing machine 100 may be a single-end pointing machine, or a
double-end pointing machine. FIG. 10 shows a representation of a
single-end pointing machine. In an embodiment of a single-end
pointing machine 100, the die 106 may be stationary and an end of a
tube 28 may be pressed into the die by the drive 102. In an
alternate embodiment of a single-end pointing machine 100, the tube
28 may be stationary and the die 106 may be pressed against an end
of the tube. The tube 28 may be repositioned in the single-end
pointing machine so that the opposite end of the tube may be
pointed.
In an embodiment of a double-end pointing machine, two dies 106 may
be separated by a distance that allows a tube 28 to be inserted
into the machine 100. The machine may be activated to point the
ends of a tube 28 positioned between the two dies 106. In an
embodiment, the tube 28 is moved against one of the dies 106 to
point the first end, and then against a second die to point the
second end. In an alternate embodiment, the tube 28 is stationary,
and the dies 106 are moved against the ends of the tube to point
the tube. A double-end pointing machine may also be formed wherein
one of the dies 106 is stationary, and wherein the other die is
moveable. A first end of the tube 28 may be pointed by moving the
tube into the stationary die. A second end of the tube 28 may be
pointed by moving the moveable die against the second end of the
tube.
Pointing a tube 28 may establish a variable wall thickness in the
pointed section of the tube. FIG. 13 shows a cross sectional view
of an embodiment of a pointed tube 28. A frustro-conical portion 66
of the pointed tube 28 may have a gradually increasing wall
thickness. The wall thickness may be least near a large diameter
end of the frustro-conical portion 66, and greatest near the
reduced diameter cylindrical portion 68. The reduced diameter
cylindrical portion 68 may have a substantially constant wall
thickness. The wall thickness of the reduced diameter cylindrical
portion 68 may be greater than a wall thickness of other portions
of the tube 28.
Un-textured, reduced diameter cylindrical portions 68 may allow
several tubes 28 to be closely spaced together within heat
exchanger 200. FIG. 14 shows an embodiment of a tube and shell heat
exchanger 200. A tube and shell heat exchanger 200 may include
shell 202, textured tubes 28, end caps 204, first fluid lines 206,
second fluid lines 208, and spacers (not shown). The first fluid
lines 206 and the second fluid lines 208 may be input and output
lines for heat exchange fluids. The lines 206, 208 may be coupled
to heat exchanger fluid lines so that the heat exchanger 200 has a
co-current or a counter-current fluid flow arrangement. The type of
flow arrangement may be chosen based upon the specific requirements
needed for a heat transfer system. Spacers may be positioned
between the shell 202 and the tubes 28, and between several
adjacent tubes. Spacers positioned between the shell 202 and the
tubes 28 may reduce the amount of space between the shell 202 of
the heat exchanger 200 and the tubes 28 to inhibit fluid channeling
in spaces adjacent to the shell. Spacers positioned between
adjacent tubes 28 may reduce the amount of space between the
adjacent tubes to inhibit fluid channeling within the spaces.
Textured tubes 28 may be coupled to support structures 210 within a
heat exchanger 200. FIG. 15 shows a sectional view of a
tube-in-shell heat exchanger 200 wherein the support structure 210
is a tube sheet. The hidden lines of FIG. 15 represent the
unreduced diameter portions of the tubes 28. If the tubes 28 are
not pointed, the unreduced diameter portions of the tubes would
need to be sealed to the support structure 210. The close spacing
of the tubes 28 would not provide much working room to seal the
tubes to the support structure 210. Further, if the tube 28 is
textured across the entire length of the tube, the texturing may
interfere with the formation of seals between the tubes and the
support structure 210. The un-textured, reduced diameter
cylindrical portions 68 may allow the tubes 28 to be easily sealed
to the support structure 210 of the heat exchanger 200. Tubes 28
may be sealed to a support structure 210 by several different
methods; including, but not limited to, welding and application of
a sealant.
FIG. 16 shows a cross sectional view of a portion of a heat
exchanger 200. Un-textured, reduced diameter sections 68 of the
tubes 28 are sealed to the support structure 210 by welds 212. The
increased wall thickness of the un-textured, reduced diameter
sections 68 may provide strength and support for the tubes 28 of
the heat exchanger 200.
Further modifications and alternative embodiments of various
aspects of the invention will be apparent to those skilled in the
art in view of this description. Accordingly, this description is
to be construed as illustrative only and is for the purpose of
teaching those skilled in the art the general manner of carrying
out the invention. It is to be understood that the forms of the
invention shown and described herein are to be taken as examples of
embodiments. Elements and materials may be substituted for those
illustrated and described herein, parts and processes may be
reversed, and certain features of the invention may be utilized
independently, all as would be apparent to one skilled in the art
after having the benefit of this description of the invention.
Changes may be made in the elements described herein without
departing from the spirit and scope of the invention as described
in the following claims.
* * * * *